I had a MPI relay go bad. Driving down the highway and "click" ( i couldn't really here it) ...dead.
I got a bad ECU code <img src="/forums/images/graemlins/confused.gif" alt="" />.
After installing my spare ECU and still nothing. Just took a lucky guess and pried the can off the relay and it was all green with corrosion.
Diamantes and Sonatas use the same relay so check the yards. I think the relay is like $75 from the dealer.

dave h.
'89 Raider V6 5spd;Aisin Hubs;; Gen2 LS: frt. brakes, rear coils;U.C.arms;R.trailing arms;idler arm; rear LSD axle w.disc brakes ;2 battery system for Dog's fan; relocated ECU; custom bumpers;J.Baker receiver;Conferr roofrack; t-bar crank.